FAQs

Can I run a 90 VDC output with a 230 VAC input?
It is always best to use a motor with an armature voltage rating that closely matches the AC voltage being used but if absolutely necessary, a 90VDC motor can be used. The motor will run warmer so it is recommended that the motor be de-rated. It is also better to use a PWM type drive instead of an SCR drive due to the superior DC form factor of PWM drives.

What is signal isolation?
In motor drive applications it is sometimes necessary to send an analog speed command signal to a drive. In those cases it is very important to make sure that either the output of the device sending the signal, or the input of the device receiving the signal, is isolated. Having input or output isolation is an added feature and is typically noted on the data sheet of the respective device. Connecting two non-isolated devices together will cause catastrophic damage to both devices. If neither device has isolation, a stand-alone isolation module, such as our ISO202 card, can be used.

What is a voltage follower?
A voltage follower is a device that can be commanded to perform a certain function via an analog control signal. In a motor and drive application, a voltage follower would be a drive that is setup to follow an external voltage as the main speed or torque command signal.

What is the difference between the armature and the field outputs?
The armature output of a drive is the main channel for power delivery to a DC motor. The armature output is meant to send variable DC voltage to the armature winding of a DC motor to create rotation. The field output of a drive is a channel of fixed voltage meant to energize the field winding of a shunt-wound motor. Energizing the shunt winding of a motor creates a magnetic field similar to that of magnets in a permanent magnet motor. It is extremely important not to wire the armature winding of a motor to the field output of a drive as this will cause catastrophic damage.

Do I have to have my motor connected when measuring the DC armature output?
If using an SCR type drive, you can measure the armature output without a motor being connected. If using a PWM type drive, a load will most likely be required to accurately measure the armature output. Please note some inexpensive volt meters might inaccurately display the armature output voltage regardless of the type of drive and load. A meter rated as a true RMS meter is recommended.

My application calls for frequent starting and stopping. What’s the best way to accomplish this?

1. Most drives have inhibit or enable functions that can be used to start and stop a motor without having to remove main power from a drive. These features can be actuated via the use of a dry contact logic relay or switch, and on some drives an NPN open collector can be used.
2. If braking a motor to a stop is required, a regenerative type drive is best suited for such an application. Regenerative type drive can brake a motor to a stop or can rapidly reverse (plug reverse) the direction without the need for power contactors, switches or brake resistors.

What is the inhibit/enable function?
The inhibit and enables functions are both methods for removing/preventing power to the motor, while leaving the drive powered. The inhibit is used to stop the motor as quickly as possible. For non-regenerative drives, this means a natural coast. For regenerative drives, these means the drive will regeneratively brake the motor, usually bypassing the DECEL trim pot circuitry. The enable is used on regenerative drives to coast the motor to a stop.

Can I use the inhibit as a brake in an emergency stop setup?
Using the drive’s logic functions should never be used in any type of emergency stop setup. The only way to prevent a motor from running is to completely remove power from the drive.

How is a thermal overload switch used?
Thermal overload switches can be used to inhibit the output of a drive in order to prevent a motor from being damaged by an overload condition. The thermal switch would have to be a dry contact type. On most drives a switch closure is required on the INHIBIT input to initiate an inhibited state. Some drives give you the option to open or close a switch to initiate the inhibit condition.

What is tachogenerator (tach) feedback?
A tachometer device, in motor drive applications, is essentially a small DC motor. The tachometer is designed to produce an analog voltage directly proportional to the rotational speed of its shaft. The shaft of the tachometer is typically coupled to the shaft of a larger DC motor. The tachometer voltage is read by a motor drive and is used as speed feedback. Tachometer feedback greatly improves the speed regulation of a motor and drive system.

What is a hall sensor?
A hall sensor is a powered device typically coupled to the shaft of a motor. As the motor shaft spins the hall sensor generators a specific amount of voltage pulses for every revolution of the motor. The pulses of voltage are read by another device. In motor drive applications, hall sensors are used as motor speed feedback devices.

What is a magnetic pick-up?
A magnetic pickup is a non-powered device typically used in conjunction with a metal gear mounted on a motor shaft. The magnetic pickup is placed in close proximity to the gear. As the motor spins and the gears teeth pass through the magnetic field of the sensor, a small output signal is generated. The signal is read by another device. In motor drive applications, magnetic sensors are used as motor speed feedback devices.

What is an encoder?
An encoder in a powered device typically coupled to the shaft of a motor. As the motor shaft rotates, the encoder generates a specific count of voltage pulse for every revolution. Those encoder pulses are then read by another device, such as our CLD100-1, and used as speed feedback. Encoders are offered in many different counts per revolution. In motor drive applications, an encoder is most commonly used as motor speed feedback to close the loop of a normal open-loop system. A device such as our CLD100-1 can be used to read encoder pulses. The CLD100-1 in turn generates an analog speed command signal for use by a drive. Using an encoder and CLD100-1 greatly improves the speed regulation of a motor and drive system.

What is a line filter?
A line filter is a device typically connected in between the AC line source and the input of a drive. A line filter is designed to prevent electrical noise from entering a drive. Line filters are commonly used in applications where electrical noise is generated, such as in welding applications. SCR type drives are most commonly affected by line noise due to their reliance on a clean AC waveform for switching purposes.

What is DC Injection Braking and how does it work?
When AC voltage is removed from a motor, it coasts to a stop. The time it takes to coast to a stop is dependent on the motor and load. DC injection braking is a method of decelerating the motor at a faster rate than it would with a natural coast. The drive applies a DC voltage across the AC motor windings, creating a constant magnetic field which in turn applies a constant torque on the rotor, causing the motor to decelerate more quickly.

How does the UV TRIP work?
The under voltage trip circuit constantly monitors power into the drive. If line voltage drops below a level which will prevent the drive from functioning properly, the UV TRIP circuit will initiate a fault condition and the output to the motor will cease. Some drive’s UV Trip circuit can be setup to try to restart once the fault condition clears.

Do I have to have a speed pot connected in order to run the motor?
You don’t necessarily need a speed pot. On most drives a series of resistors to simulate the presence of a 10K ohm speed pot is enough. If only maximum speed is desired, shorting the S2 terminal to the S3 terminal on most drives will cause the output to be at maximum. Since the input circuits of our drives vary in design, it is best to consult with the factory for proper wiring instructions

How do I reverse my single quadrant drive?
DC motor reversal can be achieved by swapping the motor lead connections to the drive. If you’d like to incorporate a reversing switch or relay, it is highly recommended that you follow these steps. A wiring diagram of this operation can be found in the manual of most drives.

1. Disconnect the motor from the drive.
2. Place a brake resistor across the motor if you’d like the motor to stop faster than it would if you let it coast stop.
3. Set the output of the drive to zero or activate the drive’s output INHIBIT function.
4. Once the motor has stopped, reconnect the motor leads to the drive in the desired polarity.
5. Set the output of the desired speed or deactivate the drive’s output INHIBIT function.

Do you have drives with “Three Wire Start/Stop” capability?
Yes, our MHS403-1.5, MHS403-10, and MHS403-25 have that feature.

Why is my CURRENT LIMIT LED always on when the motor is turning?
If the current limit LED is on, the motor has been loaded to the point where the current limit circuit has begun to work. Check motor current to make sure it has not exceeded the rating of the motor or drive. If the current level is below the rating of the motor and drive, the current limit level might have been set too low. Turn the Current Limit trim pot further clockwise to increase the current limit level.

Why does my drive not run the motor?
This is one of the questions we are most frequently asked. While a bad drive is certainly a possibility, there are several things you can do to insure you are looking in the right place for the root cause of the problem.

1. Line power: Make sure the drive you are running is actually receiving power. The best way to accomplish this is to measure your supply voltage as close as possible to the drive, ideally right at the L1 and L2 terminals.
2. Proper connection of motor: If the motor leads are not connected directly to the drive terminals, any device external to the output of the drive can be a potential suspect. Most DC motors have an armature resistance that is in the 10s of ohms or less. Measure the motor resistance right at the drive and if you measure an open, the problem is not the drive. Check motor relays, plugs, connectors, conduit boxes, etc.
3. Control Signal: Make sure the drive is actually receiving a command signal to make the motor run. If a speed potentiometer is being uses, measure across the CCW terminal and the center terminal to see if you get a linear increase or decreases in the command signal as you very the position of the potentiometer. If an external command signal is being provided, make sure it varies in the way you’d expect.
4. Enable/Inhibit: Some application may use inhibit or enable commands. Make sure the drive is not being commanded to NOT put out motor voltage. Most drives have inhibit terminals and some have RUN/BRK or Enable terminals.
5. Trim pot adjustments: Some adjustments on the drive can cause motor voltage not to be present. The Current Limit/TQ pot when set too far CCW can cause the motor to stall as soon as it demands current. For testing purposes, the TQ can be set full CW to allow for maximum current if needed. The Maximum Speed trim pot if set too far CCW can also cause the motor voltage to be low, and on some drives, non existent. For test purposes, turn the Maximum adjustment to full CW.
6. Input Voltage Selector Switches: While many of our drives have auto ranging power supplies, some of our drive require you setup the drive to accept either 115VAC or 230VAC.

Why does my drive keep blowing fuses / tripping breakers?
A defective drive can definitely cause fuses of breakers to trip. Since the drive conducts the same amount of current as the motor, it is one of the most stressed components of a drive system. In most cases, drives do not simply go bad but rather are stressed to the point of failure. Locating the source of the stress is the key to correcting the problem.

1. Grounded motor: Check to make sure the motor has not become grounded by checking the resistance from each terminal of the motor to earth ground. If using an ohm meter, the resistance to ground should be in the Megs of ohm’s or essentially an open. A motor’s internals can either permanently or momentarily short to the case. A grounded motor will almost instantly cause permanent drive damage giving you the false impression that the drive is the source of the problem.
2. Line Power: Make sure line power is clean. Certain drives are more susceptible to problems caused by “dirty” line voltage as they may use certain portions of the 60Hz line as a clock. Line power can be distorted by the cycling of large machines, motors, pumps or welding operations. AC line filters can help maintain a clean AC waveform.
3. Wiring: If using a field or shunt wound motor, connecting the armature winding of the motor to the field output of the drive will permanently damage the drive and give you the false impression that the drive is the problem. Even if the motor is disconnected, a damaged drive will continue to blow fuses or trip breakers.
4. Speed command signal: If using an external command signal to control motor speed, make sure the signal is isolated or make sure the drive has input isolation. Connecting two non-isolated devices together will cause damage to the drive and the device providing the signal.
5. Overloading: Exceeding the drives current rating or ambient operating temperature can stress the drive to the point of failure. Monitor motor current to make sure it is within the level you expect and not exceeding the rating of the drive. If the drive is in an enclosure, adding forced air will help insure the drive is operating within the ambient rating.

Why does my motor run at full speed all the time?

1. Speed command signal: Make sure the command signal to the drive is not set to maximum. If a speed potentiometer is being used, make sure the pot is not open, miss wired or has an open terminal.
2. Minimum speed setting: Most drives have a minimum speed adjustment that is independent from the main speed command signal. Make sure the minimum speed trim pot has not been turned up.
3. Tachometer feedback: If using tachometer feedback, make sure the drive has been setup to accept the tachometer feedback. If already set to accept the feedback, make sure the drive is receiving tachometer voltage right at the tachometer inputs of the drive. With regenerative drives, the polarity of the tachometer signal is very important.

Why does my motor oscillate / not run smoothly?

1. IR Comp Adjustment: Most drives have this adjustment. If set too far clockwise the motor will tend to oscillate. Slowly turn the IR Comp trim pot in the counter clockwise direction until the oscillation stops.
2. Speed command signal: An unstable speed command signal to the drive can cause the motor not to run smoothly. Remove the command signal from the drive and use a potentiometer instead. If the motor becomes smooth, the external speed command signal was the source of the problem.
3. Change in load: In most applications a drive can be tuned to run a motor smoothly and compensate for changes in load. But when loads change abruptly, the IR Comp circuit cannot respond fast enough. Make sure there are no mechanical problems in the operation that can cause these abrupt changes in load. A good way to check this is to simply remove the load from the motor and observe how it runs. If operation becomes smooth, you most likely have a mechanical obstruction.
4. Motor brushes: If using a permanent magnet motor, inspect the brushes for excessive wear or irregular wear. It also a good idea to blow compressed air into the brush housing to clean out any carbon build up. If possible, turn the motor shaft as you blow compressed air into the brush compartment.
5. Max speed too high: Having the output voltage to the motor set too high can cause some drives armature output to become unstable. Do not try to run a motor that exceeds the armature voltage that is available to use. For example, you can’t run a 180VDC rated motor when you power a drive with 115VAC.

Why is my motor running at twice it’s rated RPM?
When the magnets in a PM type motor become demagnetized, the result is an increase in motor speed with reduced torque. Magnets tend to gradually lose their magnetism under normal use but this can be accelerated by continuously overloading a motor.

Why does my motor not seem to have enough power and stall easily?

1. Since most drives are designed to run a wide range of horsepower motors, it is important to calibrate the Current/TQ limit to match the motor being used. If the limit is set too low, the motor will not be allowed to draw enough current to perform its job. A drives user manual typically has approximate setting for various HP motors. In most cases, setting the current limit to 100-150% of the motors continuous duty rating will be adequate.
2. Check to make sure the motor is sized properly for the application. An undersized motor will not be able to perform the work required regardless of how much current you allow it to draw. Measure the motor current draw and if it exceeds the continuous duty rating, the motor may be too small.
3. AC motors drives tend to have a boost adjustment that when turned up will provide an extra boost of current at the lower end of the speed range to help move loads that are stationary.

Why is my motor producing a loud humming/buzzing sound?
If the motor is producing this type of sound, a non-filtered SCR type drive is probably being used to run it. SCR type drives pulse a motor with voltage 120 times per second. The sound that is heard is the magnetic fields energizing and breaking down inside the motor at 120Hz. Although this is normal, a PWM type drive is a good choice if the hum is not acceptable in the application.

Why is my motor running backwards?
If using a single phase AC motor, swap one of the windings (connection may be internal to motor).
If using a three phase AC motor, swap any two of the three leads.
If using a DC motor, swap the armature wires.

What is the MIN SPD trim pot and how is it used?
The MIN SPD adjustment allows you to set a minimum speed when your main speed potentiometer is set to the full counter-clockwise position. To set minimum speed you must turn your main potentiometer full CCW. Once that is done, turn the MIN SPD trim pot clockwise until the desired minimum speed is reached. This adjustment is useful in an application where you may want your motor to run even if your main pot is set full CCW.

What is the MAX SPD trim pot and how is it used?
The MAX SPD adjustment allows you to set the maximum speed when your main potentiometer is full CW. In some application, it may be desirable to run the motor at a lower speed than maximum. To set maximum speed you must adjust your main potentiometer full CW. Once that is done, turn the MAX SPD either CW or CCW until the desired maximum speed is reached.

What is the ACCEL trim pot and how is it used?
The ACCEL adjustment allows you to ramp up the speed of a motor to the commanded speed rather than having the motor abruptly go that commanded speed. Setting the ACCEL trim pot at the full CCW position will result in the fastest ramp up to the commanded speed. Turning the trim pot clock-wise will result in the motor ramping up slowly to the commanded speed. Having this adjustment is useful in applications where an abrupt start of the motor may cause undesired effects. Injecting an ACCEL ramp also helps the mechanical components of a drive system by not causing sudden stresses on pulleys or gears.

What is the DECEL trim pot and how is it used?
The DECEL adjustment allows you to ramp down the speed of a motor rather than having the motor stop or slow down abruptly when going from a high speed to slower speed. When using a single quadrant drive, the deceleration trim pot will have no effect on a motor with a high inertia or overhauling load. On a load that would otherwise cause a motor to slow down or stop faster than desired, turning the deceleration trim pot CW will cause the drive to slowly ramp down the voltage to the motor.
When using a four quadrant drive, the deceleration trim pot will work as noted above with high inertia loads as well as with high friction loads.

What is the advantage/disadvantage of a single ACCEL/DECEL trim pot?
An advantage would be the simplicity of adjusting one trip pot and setting both acceleration and deceleration. A disadvantage would be that you will not have independent adjustments for applications that require different ramp up and ramp down times.

What is the IR COMP trim pot and how is it used?
The IR COMP is a circuit designed to send a voltage boost to the motor only when it is under load. The voltage boost helps keep the no load and full load RPMs of the motor as consistent as possible. When a motor is under load it will demand more current. When the drive senses that current draw it sends a voltage boost to the motor proportional to the current draw. The ratio of voltage boost to current draw can be adjusted via the IR COMP trim pot. Turning the IR COMP trim pot CW will increase the voltage boost at any given load. Turning the IR COMP too far CW can cause overcompensation and the motor may oscillate.

What is the CURRENT LIMIT trim pot and how is it used?
Current Limit is a circuit designed to limit the amount of current a motor can draw in the event of an overload condition. Without a current limiting circuit a DC motor could draw several times its rated current. If the overload condition was not cleared in a timely manner, a motor could suffer severe damage. Setting the current limit properly can provide more time to identity and clear overload conditions. The Current Limit circuit constantly monitors the amount of current a motor demands. If the motor current draw exceeds the limit set by the Current Limit trim pot, the drive begins to lower the amount of voltage it sends to the motor. By lowering the voltage to the motor, the drive is essentially limiting the current. If the overload condition gets worse, the drive will further reduce the voltage it sends to the motor. Turning the current limit CW increases the current limit level the motor will be allowed to draw.

What is the TORQUE LIMIT trim pot and how is it used?
See "What is the CURRENT LIMIT trim pot and how is it used?"

What is the TQ LIMIT trim pot and how is it used?
See "What is the CURRENT LIMIT trim pot and how is it used?"

What is the BOOST trim pot and how is it used?
The BOOST is used to increase motor torque at low speeds on AC motors. For most applications, it's not needed, but if the motor stalls or runs erratically at very low speeds, an increase in the BOOST may help.

What is the SLIP COMP trim pot and how is used?
The SLIP COMP is similar to the IR COMP, but for AC motors. It uses a frequency/voltage boost to vary the slip between the rotor and the stator to help regulate motor speed with changing loads.